Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"


namespace Rivet {


  /// @brief Add a short analysis description here
  class SND_2000_I524221 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(SND_2000_I524221);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_numEtaGamma, "TMP/EtaGamma");
      book(_numPi0Gamma, "TMP/Pi0Gamma");
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          --nRes[child.pid()];
          --ncount;
        }
        else
          findChildren(child, nRes, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {

      const FinalState& fs = apply<FinalState>(event, "FS");

      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      if (ntotal == 2 && nCount[22] == 1 && nCount[111] == 1) _numPi0Gamma->fill();


      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        // find the eta
        if (p.pid() == 221) {
          map<long, int> nRes = nCount;
          int ncount = ntotal;
          findChildren(p, nRes, ncount);
          // eta pi+pi-
          if (ncount != 1) continue;
          bool matched = true;
          for (const auto& val : nRes) {
            if (val.first == 22) {
              if (val.second != 1) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) _numEtaGamma->fill();
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 1; ix < 3; ++ix) {
        double sigma, error;
        if (ix == 1) {
          sigma = _numEtaGamma->val();
          error = _numEtaGamma->err();
        }
        else {
          sigma = _numPi0Gamma->val();
          error = _numPi0Gamma->err();
        }
        sigma *= crossSection() / sumOfWeights() / nanobarn;
        error *= crossSection() / sumOfWeights() / nanobarn;
        Estimate1DPtr mult;
        book(mult, 1, 1, ix);
        for (auto& b : mult->bins()) {
          if (inRange(sqrtS() / MeV, b.xMin(), b.xMax())) {
            b.set(sigma, error);
          }
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _numEtaGamma, _numPi0Gamma;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(SND_2000_I524221);


}